Electronic circuit by which electric current is fed to spark plugs of an engine

ABSTRACT

An electronic circuit by which electric current is fed to spark plugs of an engine, adapted to reliably operate up to about 12,000 RPM with practically no overheating. The circuit comprises two transistors and a unit, consisting of two resistances and one capacitor, for the polarization of transistor bases, as well as a diode connected between the unit and the positive pole of an electric current source.

United States Patent 1 1 1111 3,983,861

Di Cecco et a1. Sept. 9, 1975 [5 ELECTRONIC CIRCUIT BY WHICH 3,552,368 1/1971 Hunter 123/148 E ELECTRIC CURRENT IS FED o SPARK 3,599,616 8/1971 OiShi 123/148 E 3,658,044 4/1972 Safstrom 123/148 E PLUGS OF AN ENGINE 3,692,009 9/1972 Roth et a1. 123/148 E [75] Inventors: Enio Di Cecco, Milan; Mario Totti, 9 /1 rg 12 /148 E Rozzano, both f Italy 3,715,650 2/1973 Draxler 123/148 E 3,722,489 3/1973 Howardm. 123/148 E Asslgneec Safe Electronic Systems 3,808,513 4/1974 Canup 123/148 E Mauren, Liechtenstein 3,818,885 6/1974 Canu 123/148 E [22] Filed: Apr. 3, 1973 Primary ExaminerCharles .1 Myhre Assistant Examiner-Joseph A. Cangelosi Attorney, Agent, or Firm--Waters, Schwartz & Nissen [21] Appl. No.: 347,489

[30] Foreign Application Priority Data June 23, 1972 Italy 26144/72 [57] ABSTRACT U S Cl 123/148 315/209 CD An electronic circuit by which electric current is fed [51] Int Cl iiiiiiiiiiiiiiiiiiiii u FOZP 3/06 to spark plugs of an engine, adapted to reliably oper- Fieid CD ate up to about 12,000 RPM with practically no overheating. The circuit comprises two transistors and a [56] References Cited unit, cons1st1ng of two res1stances and one capac1tor, for the polarlzatlon of translstor bases, as well as 21 UNITED STATES PATENTS diode connected between the unit and the positive 3,372,682 3/1968 Phillips Ci al 123/148 E pole f an electric urrent source 3,487,822 l/l970 Hufton CI 3.1. 3,546,528 12/1970 Fisher 123/148 E 5 Claims, 1 Drawing Figure t l 8 ==3c5 csj, R6

PATENTED SEP 9 i975 i i/C5 SCR ELECTRONIC CIRCUIT BY WHICH ELECTRIC CURRENT IS FED TO SPARK PLUGS OF AN ENGINE This invention concerns a capacitive discharge electronic circuit, by which electric current is fed to spark plugs of an engine, and more particularly to the H.V. spark coil of electric circuit of the engine.

Many types of capacitive discharge electronic circuits, controlling the spark ignition system of an engine, are already known. A drawback of such circuit is to be traced back to their high electrical input, ranging from about SA, up to 5A, in operation, to which results in an overheating of some electronic components of the circuit, such as the transformer, the transistors and the thyristor, forming a part of said circuit. Such overheating, above all at higher RPMs of the engine, results in a loss of the output thereof, and may also choke, in the long run, the operation of the ignition circuit.

ln more detail, the capacitive discharge electronic circuits, by which current is fed to spark plugs of an engine, comprise a power supply unit, by which a H.V. (in the range of about 250 and 450 V) DC. is fed, having a thyristor and a capacitor parallel-connected with its outlet, said capacitor being seriesconnected with the H.V. coil for feeding said current to the spark plugs of the engine. Throughout the operation, the capacitorcoil unit, and obviously also the outlet of the power supply unit are reiteratively short-circuited for very short times. This results on the one hand in the discharge of the capacitor, and on the other hand in an increase in the current that flows through the power supply unit, due to short-circuiting thereof.

Owing to the structure of the already known circuits, both the components of said power supply unit and the proper thyristor are overheated by said increase in the current.

In the engine spark-plug feeding electronic circuits, a positive peak (which is utilized for the ignition) is firstly attained by the voltage discharge in the H.V. spark coil, such positive peak being directly followed by a negative peak, which is not of use to the ignition. Attempts were made, in the capacitive discharge electronic circuits, to recover said negative voltage by having recourse to a rectifier that forms a part of the power feeding unit; but heretofore only a small fraction of said voltage has been recovered.

A further drawback of the already known electronic circuits is that they cannot be utilized in engines runnin g at very high RPMs, and as a matter of fact they are practically utilized in engines rated up to 6,0()08,000 RPM only, since at higher RPM these circuits are easily damaged beyond rapair, because the power input increases with increasing RPM.

The main object of this circuit for consists in the provision of a capacitive discharge electronic for feeding the spark plugs of an engine, that shows a very low power input (eg about 1.6-1.7 A 6,000 RPM) even at the higher RPM of engine. Another object consists in the provision of a circuit of the above stated type wherein, when the thyristor is short-circuited, the current flowing through the power feeding unit is decreased (instead of increasing, or even remaining steady), when compared with the current flowing through same unit when this is directly connected with the battery. and the engine is inoperative, i.e.; when the ignition key is inserted and is in the ignition position while the engine is inoperative, which means that the heating of the power feeding unit, along with the electronic components that are connected therewith in the circuit, is practically negligiblewhile the engine is operated.

A futher object of the invention is the provision of a circuit wherein the negative voltage peak, occurring in the H.V. coil, is nearly wholly utilized for recharging the discharge capacitor up to a degree much higher than was heretofore possible in the already known circuits, whereby to attain a very low power input.

Another object of the invention is the provision of a circuit that can be utilized in engines equipped with electronic revolution counters, and that can properly operate even when the engine is running at very high RPM, i.e. 12,000 RPM and higher.

A further object of the invention is the provision of an ignition circuit which, even in tropical climates and under unusually severe and protracted conditions of operation, is not subjected to overheating, thus maintaining their operating features nearly unchanged.

The electronic circuit for the firing of spark plugs according to the invention Comprises a feeder-booster, connected with a capacitive discharge circuit, which in turn is connected with the H.V. coil of the circuit through which electric current is fed to the spark plugs, said feeder-booster compressing two resistors and a capacitor for the polarization of the bases of transistors which form a part of said feeder-booster,'and characterized in that in series with the feeder-booster lead which is connected with the positive pole of DC. source, is a resistor having a value ranging from about 39 and 89 and parallel connected with at least one diode; that the primary winding/reactance turns ratio of a transformer of the feeder-booster is in the range of about 1.6/1 and 2.7/1, and that the values of the two resistors and of the transistor base polarization capacitor with which said feeder-booster is fitted, are for the one resistor in the range of about 220. and 569, for the other resistor in the range of about 6000 and 1,2009, and for the capacitor in the range of about 1 and 8 mfd.

A diode is preferably connected between said two re sistors and the transistor base polarization capacitor, and the feeder-booster lead which is connected with the positive pole of the DC. source.

The invention will be disclosed in the following description of a preferred embodiment form thereof, taken with the accompanyng drawing, wherein the ole figure is a wiring diagram of an electronic circuit, both the description and drawing being given as a non non restrictive example only.

The circuitry as shown in the drawing comprises a feeder-booster connected with a capacitive discharge circuit. Said feeder-booster is shown below the broken line in the drawing, and their two terminals 1,2 can be connected with a low voltage D.C. source, e. g. with the battery of the motor car. In particular, the terminal 1 is designed to be connected with the positive pole of said battery.

The capacitive discharge circuit is shown in the upper half of drawing, above the broken line, and the lead-in and -out wires thereof, indicated by the reference numerals 3 and 4, respectively, can be connected with the terminals the H.V. coil the supply circuit of the engine to which the electronic circuit is to be fitted.

The feeder-booster comprises a booster-transformer, having a primary Winding 5 connected with two transistors T1 and T2, respectively, and a reactance winding 6, by which an oscillation is triggered, thus resulting in the generation of an alternating voltage in the secondary winding 7. By such voltage, after having been rectified by means of a bridge comprising four diodes D1,D2,D3 and D4, a capacitor C3, forming a part of the capacitive discharge circuit, is charged, The polarization of the bases of transistors T1 and T2 in the feeder-booster, is caused by two resistors R1 and R2 and by a capacitor C1, through the reactance winding 6 of the transformer.

Series-connected with the lead-in wire, leading from the positive pole of the DC. source represented by the battery, to terminal 1 of feeder-booster, is a resistor R3, in turn parallel connected with two diodes D5 and D6, respectively. To the set of components R3, D5 and D6 the very important task is assigned to give assistance to the operation of the set of elements R1, R2, C1 in the times wherein the diode S C R (forming part of considered circuit and whose function will be explained later on) is non-conductive, whereby to reduce the power input of the feeder-booster down to about 70-100 mA; thus, a high power input by the feeder-booster is prevented in those continuously repeated times when it is in a short-circuited condition, in such a way, that a significant result is attained, ie the prevention of overheating in the circuit, in particular of transistors T1 and T2 of burning-out of transformer, etc. etc.

The circuitry of the feeder-booster also comprises a capacitor C2, acting as an interference filter both at the lead-in and lead-out ends, and a diode D7, which is connected between the DC. feeding wire, or strictly stated between the terminal 1, and the set by which the bases of transistors T1 and T2 are polarized, i.e. with the set comprising the transistors T1 and T2, and the capacitor C1.

The presence of said diode D7 in the circuit is not essential for an efficient operation of said circuitry; however, it has been noted that by the presence of said diode D7 in the circuitry, a better efficiency of transis tors T1 and T2 is attained, above all at the higher temperatures. In particular, when a too high increase in the temperature of the circuitry occurs, eg when a value of 80C is exceeded, the operating features of same circuitry which would otherwise be affected are kept unchanged by said diode D7. Indeed, when the temperature increases, a decrease in the resistance of diode D7 occurs, which results in a polarization voltage increasing with the increase in the temperature being applied to the bases of transistors T1 and T2, when they are made non-conductive by the inhibition of diode SCR (which will be described in more detail later on). Thus, the current flow across the transistors T1 and T2 is reduced, whereby undesired overheating is prevented. At any rate, it is expedient to point out that the presence of diode D7 is essential only in exceptional cases, eg when the circuitry is operated at very high ambient temperatures, with high discharge frequencies and with large power inputs.

The capacitive discharge circuit, as shown in the upper half of the drawing, is designed to discharge the power received from the feeder-booster and stored in the capacitor C3, through the lead-out wires 3,4 and into the H.V. coil of the ignition system of the engine to which the electronic circuit is fitted: said power discharge function is performed by the diode SCR, that is operated by its control electrode, to which is applied a reverse or negative bias equal to one half of the voltage fed by the feeder-booster.

The application of such bias to the control electrode of diode SCR is obtained by means of two resistors R4 and R5, and a capacitor C4.

The control pulse for the diode SCR is obtained from the inductive effect of a coil L, connected between the positive lead of the feeder voltage, and the ground G, through the platinum point or movable contact 8 of the ignition distributor that forms a part of the power feeding equipment of the engine to which the electronic circuit is applied.

The positive pulse thus generated on the side of above stated platinum points 8, by means of coil L, in the moment in which said points are drawn away from each other, i.e. when they are opened, flows through the circuit consisting of the resistor R6, diode D8 and capacitor C5, and is applied to the control electrode of diode SCR, thus making it non-conductive with consequent discharge of capacitor C3.

The electric gating of diode SCR occurs instantaneously at the end of the pulse sent by the coil L; such instantaneous function is highly assisted by the reverse bias applied to the control electrode of diode SCR.

The circuit also (D mprises a resistor R7 and a capacitor C6 by which the low voltage that serves for biasing the diode SCR and for feeding the coil L is filtered out and electrically separated.

The circuit slso comprises a capacitor C7 and a resistor R8, series-connected with each other, and having the task to reduce the overvoltage peaks produced in the H.V. coil of the engine power feeding circuit, when the capacitor C3 is discharged, thus preventing damage of diode SCR; simultaneously the recharge of capacitor C3 through the bridge of diodes D1, D2, D3 and D4 is promoted.

It is to be finally mentioned that the capacitive discharge circuit also comprises a resistor R9, as shown in the drawing.

Upon closing the circuit through which power is fed to the feeder-booster, and that may be a low voltage, 12 V circuit, connected with the terminals 1 and 2 of the battery, said voltage is applied to the transformer of the feeder-booster, to the biasing set of elements R1, R2 and C1, and to transistors T1 and T2 through the primary winding of said transformer, flowing across the set of elements D5, D6 and R3, thereby causing the oscillatory triggering of the feederbooster, and delivering the voltage as required for charging the capacitor C3 at the outlet of the bridges of diodes D1, D2, D3 and D4.

As soon as the platinum points 8 are operated, i.e. when they are opened and closed, a pulse is sent to diode SCR, which is thus rendered non-conductive, thereby causing the discharge of capacitor C3 to the H.\/. coil of the engine power feeding circuit. In particular, it may be observed that, when the feed voltage is 12 V at terminals 1 and 2 and germanium transistors T1 and T2 are utilized, the value of resistor R3 should be in the range of about 3 and 89, and preferably about 5-69, it being at this point expedient to note that said resistor may possibly be switched-off by three or more diodes, rather than by only two diodes D5 and D6, as shown in the drawing.

Again on the basis of the above assumption, the turns ratio of the primary winding 5 and the reactive winding 6 of transformer is in the range of about 16/1 and 27/1, and preferably about 2/1-2. H1. The value of resistor R2 is in the range of about 22 and 56D and preferably about 330, while the value of resistor R1 is about 600 12009, preferably about 820Q. The value of capacitor C2 is in the range of about 1 to 9 mfd, and preferably about 35 mfd.

The required high efficiency of the electronic ignition circuit can be attained, even under the most severe operating conditions, and at high ambient temperatures, only with the above stated values for the components of the disclosed electronic circuit, on the basis of the above assumption of feeding at 12 V and in particular with the presence of set of elements D5, D6, R3.

The inductance of coil L, which presence is essential only when the engine, fitted with the circuit according to the invention, is provided with an electronic revolution counter, but which is at any rate useful to apply a high reverse polarization to diode SCR, should be in the range of about 70 and 280 mH, and preferably about 180 mH. The winding of said coil should preferably be of the honeycomb or lattice type.

The value of resistor R8 should be about 200 and 8009, and preferably should about 4709, while the value of capacitor C7 should be in the range of about 8,000 and 30,000 pfd, and preferably should be about 22,000 pfd.

Finally, particular mention is made of the feature of relatively high negative voltage by which the diode SCR is biased, such voltage being obtained owing to the presence of resistors R4 and R5. Applied to said diode is thus a negative bias voltage equal to about one half of the voltage delivered to the feeder, and that is assumed to be of 12 V.

Again in the case wherein a 12 V direct voltage is fed to terminals 1 and 2, and when the transistors are of the silicon type, the resistor R3 should have a value ranging from about 0.5 to 89, and preferably from about 0.1 to 60, while the values of both resistors R1 and R2 should be in the range of about 200 12000, and about and 56!), respectively, and preferably about 300-8009, and 15-330, respectively. The inductance of coil L should conversely be in the range of about about to 280 mh, and preferably in the range of about 70180 mh.

The many and exhaustive tests to which the circuit was subjected, have proved that all objects as stated in the introductive section of this disclosure, have been fully attained.

What we claim is:

1. In an electronic circuit for the operation of engine spark plugs, comprising a feeder-booster, a capacitive discharge circuit connected to said feeder-booster and in turn adapted for connection with an H.V. coil of an electric circuit through which power is fed to the spark plugs, said capacitive discharge circuit including an SCR diode, said feeder-booster being adapted for connection to a direct current source, an improvement wherein said feeder-booster comprises a pair of transistors, a pair of resistors (R and (R and a capacitor (C connected to the bases of said transistors to bias the same, lead-in wires adapted for connection with the direct current source, a resistor (R in series connection with one said lead-in wire and having a value in the range of about 0.05 to 80, at least one diode (D or D connected in parallel with said resistor, a transformer connected to said transistors and adapted for connection to said direct current source via said resistor and diode, said transformer having a ratio of primary winding to reaction winding in the range of about 1.6/1 and 2.7/1, the values of the two resistors (R, and R and the capacitor (C,) which bias the bases of said transistors being 2002000 Q for resistor R 10-5 60 for resistor R and 1-8 mfd for the capacitor (C and a second diode (D connected between the lead-in wire connected to the positive pole of the direct current source and the set consisting of said two resistors (R,) and (R and said capacitor (C 2. An electronic circuit according to claim 1 comprising a coil having an inductance in the range of 20 to 200 mH connected between said positive pole and the circuit by which power is fed to the spark plugs.

3. An electronic circuit according to claim 1 wherein said resistance (R has a value in the range of 0.l to 69, the turns ratio of the primary winding to the reaction winding of said transformer is in the range of 2/1 to 2.1/1, and the values of said two resistors (R and (R and capacitor (C,) are in the range of 15-33Q, 300800 Q and 35 mfd, respectively.

4. An electronic circuit according to claim 2, wherein said coil connected between said positive pole and the power circuit has a value in the range of to mH.

5. An electronic circuit according to claim 2 wherein said coil connected between said "positive pole and the power circuit is of the honeycomb wound type. 

1. In an electronic circuit for the operation of engine spark plugs, comprising a feeder-booster, a capacitive discharge circuit connected to said feeder-booster and in turn adapted for connection with an H.V. coil of an electric circuit through which power is fed to the spark plugs, said capacitive discharge circuit including an SCR diode, said feeder-booster being adapted for connection to a direct current source, an improvement wherein said feeder-booster comprises a pair of transistors, a pair of resistors (R1) and (R2) and a capacitor (C1) connected to the bases of said transistors to bias the same, lead-in wires adapted for connection with the direct current source, a resistor (R3) in series connection with one said lead-in wire and having a value in the range of about 0.05 to 8 Omega , at least one diode (D5 or D6) connected in parallel with said resistor, a transformer connected to said transistors and adapted for connection to said direct current source via said resistor and diode, said transformer having a ratio of primary winding to reaction winding in the range of about 1.6/1 and 2.7/1, the values of the two resistors (R1 and R2) and the capacitor (C1) which bias the bases of said transistors being 200-2000 Omega for resistor R1, 1056 Omega for resistor R2, and 1-8 mfd for the capacitor (C1) and a second diode (D7) connected between the lead-in wire connected to the positive pole of the direct current source and the set consisting of said two resistors (R1) and (R2) and said capacitor (C1).
 2. An electronic circuit according to claim 1 comprising a coil having an inductance in the range of 20 to 200 mH connected beTween said positive pole and the circuit by which power is fed to the spark plugs.
 3. An electronic circuit according to claim 1 wherein said resistance (R3) has a value in the range of 0.1 to 6 Omega , the turns ratio of the primary winding to the reaction winding of said transformer is in the range of 2/1 to 2.1/1, and the values of said two resistors (R1) and (R2) and capacitor (C1) are in the range of 15-33 Omega , 300-800 Omega and 3-5 mfd, respectively.
 4. An electronic circuit according to claim 2, wherein said coil connected between said positive pole and the power circuit has a value in the range of 70 to 180 mH.
 5. An electronic circuit according to claim 2 wherein said coil connected between said positive pole and the power circuit is of the honeycomb wound type. 